International Journal of Mechanical Sciences最新文献

The abundance of variable cross-section curved rails in railway turnouts emphasizes the necessity of intricately modeling them, which facilitates a more accurate evaluation of train-turnout interactions. This study presents a general formulation for analyzing both free and forced vibrations of a variable cross-section curved Timoshenko beam and its implementation in train-turnout dynamic interactions. First, the natural frequencies and mode shapes for in-plane and out-of-plane free vibrations of the beam are determined through eigenvalue analysis, taking into careful consideration the characteristics of variable cross-section and curvature. Then, the forced vibration solution is derived using modal superposition and orthogonality. Furthermore, comparative analyses using finite element method (FEM) validate the natural frequencies and dynamic responses of a beam under various boundary conditions, confirming the reliability and accuracy of the proposed method. Finally, the developed beam model is then applied to simulate the switch rail and point rail under train-turnout interactions, revealing the differences from existing methods that modeled these components as uniform cross-section straight beams. Numerical analyses provide new insights by comparing wheel-rail forces and rail acceleration. Considering curve and variable cross section characteristics could contribute to a more accurate evaluation of train-turnout dynamic interactions.

Understanding the behaviour of hot jets is crucial for various engineering and environmental applications. The present work studies the influence of heat transfer on the dynamics of horizontal round hot jets through Large Eddy Simulations (LES). Our focus lies on trajectory development, large-scale coherent structures, and turbulent kinetic budget analysis in the near-field and intermediate-field regions. LES of two horizontal round hot jets with Reynolds numbers (3934 and 5100) and corresponding Froude numbers (32.98 and 17.07) were carried out using buoyantPimpleFoam solver in OpenFOAM, and the simulation on an isothermal jet was also performed as a baseline for comparison. The results reveal that the jet core temperature decays faster in the streamwise direction but more slowly in the radial direction, indicating a wider temperature spread than velocity, and the maximum difference between the temperature and velocity spread is about 0.5D. Moreover, the energy associated with the large-scale coherent structure decreases with increasing initial jet temperature. The energy of the first two modes of snapshot Proper Orthogonal Decomposition (POD) and extended POD dropped by 12% and 14%, respectively. The coherent motion with the greatest correlation between the temperature and velocity fluctuations is identified as four pairs of Q1 and Q3 events, which are Reynolds shear stress dominant events. Furthermore, compared with the isothermal jet, the turbulent kinetic energy budgets of the hot jets indicate that the diffusion and generation terms are both reduced by approximately 50%, suggesting a transfer of more kinetic energy into potential energy rather than turbulence. The finding highlights the potential of heightened temperatures to mitigate instabilities associated with large-scale motions in hot jets. This study fills the gap on a comprehensive analysis of heat transfer effects on jet dynamics, and quantitative insights into the large-scale coherent structures are provided, contributing to a better understanding of hot jet behaviour.

Understanding the fundamental mechanism of shrink hydrogel sensors necessitates a complete comprehension of analyte-centered multivalent binding that occurs within their salt-rich microenvironments. However, the mechanics and thermodynamics governing this phenomenon remain insufficiently understood. Here, we aim to derive a theoretical framework that examines the impact of temporary cross-link formation on the hydrogel shrinkage due to specific binding interaction between the fixed receptors and the multivalent analytes. As a highlight of our theory, we mathematically quantify the hydrogels’ permanent and temporary cross-links using statistical thermodynamics to describe the multivalent complexation with different binding degrees while accounting for molecular-level transport factors when predicting the sensor’s shrinking characteristics. Consequently, our theory unveils the upper bounds set by the external analyte concentration and analyte binding valency onto the actuation sensitivity of these sensors, whereby tuning the receptor density permits further modulation of their performances. These findings tightly correlate the microscopic properties of the analyte and hydrogel to the macroscopic behaviors of shrink sensors, facilitating a structured design regime for advanced biomedical applications.

Multilevel helical structures are widely used in biology and engineering fields. The multilevel helical structure exhibits interesting and complex mechanical behaviors due to the hierarchical feature and interactions between various structural scales. Herein, by extending the straight filament shear-lag model, a multi-scale damage mechanical model including the helical filament and sub-cable scales is established to investigate the mechanical behavior of the multilevel helical structure. The effect of filament breakage, contact interactions, and helical characteristics on the mechanical responses of the sub-cable is investigated. It is found that helical filaments have the higher deformation flexibility than straight filaments, thus weakening the stress transferring capacity and inhibiting filament breakage. The stress-strain curve of the helical filament exhibits a plateau region by adjusting laying angles. It is demonstrated for the helical structure level that the axial tension stiffness can be enhanced by increasing laying angles of the filament bundle and sub-cable. Axial coupling stiffness with filament damage exhibits the non-monotonic variation with sub-cable laying angles. The effectiveness of the present model is also verified by comparison with axial tensile experiments of composite wires. This research seeks to elucidate the intertwined impacts of filament damage and helical characteristics on the mechanical behaviors of multilevel helical structures.

An accurate determination of the threshold conditions to initiate cracks on aged hydrogen pipelines is paramount for ensuring energy transport safety. In this work, a finite element-based phase field method was developed to assess the crack initiation on dented pipelines while considering the hydrogen (H) impact. Theoretical and multi-physics numerical formulas were derived for prediction of the elastic-plastic fracture behavior of H-contained steel. A critical phase field parameter, ϕ=0.69, is defined for predicting crack initiation at the dent on pipelines. The presence of H within the steel decreases the threshold dent depth for initiating H-induced cracks. When the initial H concentration increases from 0 to 0.5 wppm, the maximum dent depth for crack initiation reduces from 17.5 mm to 10.7 mm. The maximum dent depth required for crack initiation reduces from 17.5 mm to 7.8 mm when an internal pressure of 8 MPa is applied on the steel pipe. The site with the maximum phase field parameter changes during indentation, implying that the location initiating cracks depends on the dent dimension. The existing criteria in ASME B31.12 standard are not applicable for predicting H-induced crack initiation on dented pipelines. This study proposes a new method to predict hydrogen-induced cracking on aged pipelines when transporting hydrogen.

This study unveils a groundbreaking development: the chain lattice structure (CLS), a unique lattice with the capability to actively adjust its size and shape for filling diverse thin-walled structures, thereby enhancing their energy absorption characteristics. Traditional lattice structures, known for excellent energy absorption, are constrained by fixed sizes and shapes post-fabrication, limiting their adaptability to various energy-absorbing structures. The CLS introduces a revolutionary lattice structure dynamically modifying dimensions and shape. Employing selective laser sintering (SLS), we craft CLS prototypes using nylon 11 material, followed by rigorous quasi-static compression experiments. The congruence between experimental and simulation analyses validates our model's accuracy. CLS actively adjusts within varying cross-sectional thin-walled square tubes, demonstrating substantial improvements in energy absorption and compression stability compared to empty tubes (ETs). Additionally, CLS adapts to diverse cross-sectional shapes, including circular, hexagonal, and triangular tubes. Comparative assessments reveal significant enhancements in energy absorption and compression stability for CLS-filled tubes. Moreover, the pre-deformed CLS model was filled with different shapes of front rails, and its axial crashworthiness and deformation pattern stability were significantly improved compared with the unfilled front rails. In summary, CLS's flexibility in adjusting to thin-walled structures of varying dimensions and shapes holds immense promise for enhancing their performance across a wide range of applications.

The primary challenge in harnessing vibration energy with piezoelectric materials is the discrepancy in frequency between the energy source and the energy generator, which lowers the efficiency of energy harvesting. To address the challenge, a piezoelectric beam under friction-induced vibration (FIV) is designed, modeled, and studied for the first time to realize the pronounced FIV contributing to energy generation by adapting the vibrations of the continuum structure to align close to its resonant frequencies. The Stribeck friction model is applied to characterize the variation of friction based on the relative sliding velocity v_r between contacting objects. The analytical solution is derived to solve the dynamic responses, and transient charging simulation validated by the experiment is utilized to assess energy output. Furthermore, parameter studies are conducted based on the validated model with regard to the material properties of the beam and piezoelectric material, electrode connections of piezoelectric patches, and friction model parameters to investigate their influences on energy output. Considering the same dimensional properties, materials with low Young's modulus E and density ρ are desired for the host structure to facilitate large dynamic strain in piezoelectric materials. With an exponential decay factor C = 8, representing optimal material contact interface, pronounced higher FIV mode can be induced leading to higher output power. A root mean square charging power $P_e^{\text{RMS}}$ of 42.4 mW and a peak instant charging power P_{e − peak} of 263 mW can be achieved. In the current study, the model is implemented on a beam coupled with one piezoelectric patch, which has potential applicability to non-uniform beams with various layouts of piezoelectric patches. The presented model enables efficient optimization of continuum structural design for higher piezoelectric energy generation under friction.

Hydrogen-induced-cracking initiates without external loading due to residual stresses. Pipe manufacturing process composed of crimping, $U$-ing, $O$-ing, and expansion has a major impact on local hydrogen concentration, as strain pattern evolves from one forming step to another, causing residual stresses that serve as driving force for hydrogen diffusion. The novelty of the presented work lies in the development of a multi-scale approach that links the residual stresses from the macroscopic pipe-forming process with locally dissolved hydrogen atoms in microstructure under the consideration of microstructural heterogeneities to identify areas susceptible to hydrogen-induced-cracking. First, a 3d-pipe-forming-model was built. Second, representative volume elements with lattice defects were generated to analyze hydrogen trapping in microstructure. Third, representative volume elements were placed in the pipe via sub-modeling, so that local loading history of the pipe was assigned to microstructure models. At the end of the pipe-forming process, representative volume elements were loaded with hydrogen on the surface and final hydrogen concentration was simulated based on residual stresses, considering microstructural effects such as grain size/shape, crystallographic texture and hydrogen traps, e.g. dislocations, voids and inclusions. On meso-/macroscale, a combined isotropic–kinematic hardening material model was implemented, while on microscale, a phenomenological crystal-plasticity-hydrogen-diffusion model was coded. According to the multi-scale simulations under the consideration of microstructural effects the bottom center position in the pipe was detected to be critical to hydrogen-induced-cracking as the maximum local hydrogen concentration was predicted at that location. Based on the loading history hydrogen-induced-cracking susceptibility increases from voids to hard and soft non-metallic inclusions.

In this paper, a magnetically controlled multifunctional smart material system based on magneto-sensitive shear thickening fluid (MSTF) is proposed for the safety-enhanced lithium-ion battery (LIB) modules. The rheological behavior of the MSTF can be intelligently manipulated by a magnetic field, allowing its function in the battery module to be actively and rapidly switched between cooling and impact resistance. To quantitatively assess the temperature control and impact resistance of the purposely prepared MSTF, comprehensive experiments are conducted to thoroughly analyze the thermal performance, mechanical response, and electrochemical performance of the battery module integrated with cooling and active impact protection. The results of the cooling test show that the water-based MSTF without a magnetic field has a flowability that gives it similar temperature control to that of a commonly used coolant (water). This suggests that the MSTF can be an effective cooling medium for rapid cooling of LIBs. The results of the impact test indicate that MSTF in a magnetic field can completely avoid battery deformation and significantly reduce the impact force applied to the LIB during impact, due to the fact that the magnetic field can quickly transform the MSTF into a solid-like state, which gives it a significant anti-impact effect. More importantly, the LIBs protected by the MSTF exhibit no rapid capacity degradation or abnormal temperature increase in the subsequent electrochemical cycling tests, while the unprotected or weakly protected LIBs compromise after the impact. With the MSTF, excellent cooling and anti-impact functions can be actively switched in one system, and this innovative integrated design is expected to drive significant advances in safety for battery modules.

Layered structures are prevalent in both natural environments and engineered composite materials. The elastic bending behavior of these structures is primarily governed by properties of their abundant interfaces. While the behavior of two- and three-layered beams has been extensively studied, this research shifts the focus to the impact of elastic shearing at interfaces on the deflection of multilayered structures comprising a substantial number of layers. We present an analytical solution indicating that the bending properties of multilayered beams and plates are nonlinearly dependent on interfacial stiffness. Denoting S_e as the effective bending stiffness of an n-layered beam of length L, and S₀ as the bending stiffness of a perfectly bound counterpart, we arrive at $\frac{S_e}{S_0}=\frac{1}{1+\left(n^2-1\right)\frac{\tanh \alpha L}{\alpha L}}$ where αL represents a dimensionless parameter related to geometry and material properties. The analytical solutions, validated through finite element simulations, highlight the substantial variations in stiffness across different layered structures. This solution could also be instrumental in assessing interfacial damage and delamination in lamellar composites.